zig fmt: ignore hidden files and directories

rather than ignoring specifically "zig-cache" and "zig-out". The latter
is not necessarily the install prefix and should not be special.

The former will be handled by renaming zig-cache to .zig-cache.

Author: andrewrk

lib/compiler/fmt.zig

@@ -236,7 +236,7 @@ fn fmtPathDir(
     while (try dir_it.next()) |entry| {
         const is_dir = entry.kind == .directory;
 
-        if (is_dir and (mem.eql(u8, entry.name, "zig-cache") or mem.eql(u8, entry.name, "zig-out"))) continue;
+        if (mem.startsWith(u8, entry.name, ".")) continue;
 
         if (is_dir or entry.kind == .file and (mem.endsWith(u8, entry.name, ".zig") or mem.endsWith(u8, entry.name, ".zon"))) {
             const full_path = try fs.path.join(fmt.gpa, &[_][]const u8{ file_path, entry.name });